Ophthalmic devices such as a visual field analyzer, fundus camera, scanning laser ophthalmoscopy, optical coherence tomography (OCT) imager, and other instruments, have been traditionally operated in a clinical setting and by qualified medical professional. Eye alignment has remained a challenging problem for these devices. In order to keep the patient's head in a fixed position and distance from the device, there typically involves a structure frame with a head rest and a chin rest, on which the patient can rest the forehead and the chin.
When a visual field analyzer is used, the patient is presented with a series of light stimuli of varying intensities in different visual field locations, and the sensitivity of the retina is assessed based on the patient's ability to consciously detect and respond to these stimuli. The visual field test requires one of the patient's eyes be covered with a patch and the gaze be fixed on a spot in the center of the visual field. In order to obtain a successful map of the visual field, the patient must be able to maintain a fixed head position in relation to the test instrument and a constant gaze toward the fixation. However, even with today's computer assisted perimeter, it normally takes 5 to 10 minutes to complete the test on one eye. The influence of a patient's fatigue on the test results cannot be underestimated and remains a major challenge for test reliability and accuracy. It also happens that the patient's eye moves suddenly, such as blinking, saccades, etc., at the moment the stimulus is presented, and thus directly affects the test results.
In another option, a fundus camera is used. The fundus of the eye is the interior surface of the eyeball, including the retina which functions as a light-sensitive screen, the optic disc which is the head of the nerve to the eye, and the macula which is the small spot in the retina where vision is keenest. The device used to capture a photograph of the fundus, often expensive and sophisticated, is called Fundus Camera. To obtain high quality fundus photography can be very challenging. Any misalignment of the patient's eyeball to the imaging optics may lead to unacceptable results. Furthermore, the patient's unconscious head and eye movement can also happen at the moment when the medical staff presses the capture button, resulting in an unsuccessful attempt. However, none of the fundus cameras in the market today can effectively alleviate the problem because the device operator could not anticipate the patient's possible reaction. As a matter of fact, the quality of the fundus photography highly relies on the experience and skills of the device operator, which has hindered the device's usage, particularly in areas where the trained medical professionals are not easily accessible.
In another instance, a scanning laser ophthalmoscopy (SLO) is used. The SLO is an imaging technology that scans a focused laser beam point by point or line by line on the retina and then captures the reflected light to construct an image of the retina. Due to the scanning mechanism, it usually takes a few seconds to obtain a complete SLO image, and thus the patient's head and eye stability is even more critical in order to obtain an SLO image of good quality. In fact, some instruments have to employ a technique so-called retina tracking to dynamically adjust the scanning spot following any head and/or eye movement at a cost of system complexity and expense.
In another instance, an optical coherence tomography (OCT) imager is used. Similar to the SLO, the OCT also scans a focused laser beam point by point on the retina/cornea, and then the scattered light from the retina/cornea tissue is combined with the light from a reference arm in a low-coherence interferometer, and a cross-section image of the retina/cornea is reconstructed based on the interference patterns. Due to the scanning mechanism, OCT also requires a few seconds to complete the scan and consequently faces the same challenges as the SLO in regards to the patient head/eye movement.
Traditionally, the ophthalmic devices described above, are designed to be used by a trained operator. The patient is expected to follow the instruction from the operator passively, except pressing the response button during a perimetry test. Even after being requested to stabilize his/her head and fixate his/her eye gaze throughout the test, the patient's eyes could move involuntarily at any moment, and the head could drift away from the device with a grasp of breath. All these factors make the traditional ophthalmic exams non-trivial even with a trained operator.
What is desired is a wearable, head mounted, ophthalmic device platform that enables the patient to align him or herself to the optical system of the device, and obtain quality test results without any medical personnel or another person's assistance.